The present invention relates to a weight detector installed in vehicle seats.
Vehicles are equipped with airbags to protect passengers. A seat provided with an airbag includes a weight detector. The weight detector is used to detect whether a passenger is sitting on the associated seat and to adjust the amount of gas generated in order to inflate the airbag in accordance with the weight of the seated passenger. Japanese Unexamined Patent Publication No. 11-304579 describes an example of a weight detector.
A typical weight detector includes load sensors attached to a lower portion of a vehicle seat. The load sensors are located in the four corners of the seat to detect the weight of a passenger seated on the seat. Load is applied to and detected by each load sensor. The sum of the loads detected by the sensors represents the weight of the seated passenger. The detection is used to determine whether a passenger is sitting on the seat and whether the seated passenger is an adult or a child.
It is preferred that the sum of the loads detected by the load sensors does not fluctuate regardless of the state of the vehicle. In other words, it is preferred that the sum be a constant value even when the state of the vehicle changes the load detected by each sensor.
FIG. 6(a) is a graph illustrating the optimal load fluctuation characteristic of each load sensor when the vehicle is turned right. The load detected by the load sensor located at the rear left side of the seat increases when the vehicle is turned right and decreases as the vehicle is straightened, as shown by curve RL. The load detected by the load sensor located at the rear right side of the seat decreases as the vehicle is turned right and increases as the vehicle is straightened, as shown by curve RR.
The load detected by the load sensor located at the front left side of the seat substantially remains constant regardless of whether the vehicle is turned right, as shown by curve FL. The load detected by the load sensor located at the front right side of the seat also substantially remains constant regardless of whether the vehicle is turned right, as shown by curve FR.
The sum of the loads detected by the load sensors, which are respectively represented by the curves RL, RR, FL, FR, remains constant, as shown by curve T. That is, the sum is constant because even when the detected loads respectively shown by the curves RL, RR greatly fluctuate, the curves RL, RR offset one another.
Accordingly, the weight detection is accurate regardless of how the vehicle is steered as long as the load sum is based on values obtained by load sensors having characteristics that enable the detection represented by the curves RL, RR, FL, FR as shown in FIG. 6(a).
However, each load sensor has a predetermined detection range. Thus, when the load applied to the sensor is not included in the detection range, the sum of the detected loads fluctuates.
FIG. 6(b) is a graph illustrating load fluctuation characteristics of load sensors having a limited detection range when the vehicle is turned right. The load sensors, which are arranged at the four corners of the seat, detect loads in the range of minimum value L1 to maximum value L2 (e.g., xe2x88x9210 kg to 50 kg).
In FIG. 6(b), as shown by curve RL, the load detected by the load sensor located at the rear left side of the seat increases until reaching the maximum value L2 when the vehicle is turned right. The detected load remains at the maximum value L2 until the actual load decreases to the maximum value L2 as the vehicle is straightened.
As shown by curve RR, the load detected by the load sensor located at the rear right side of the seat decreases until reaching the minimum value L1 when the vehicle is turned right. The detected load remains at the minimum value L1 until the actual load increases to the minimum value L1 as the vehicle is straightened.
The load detected by the load sensors located at the front left and right sides of the seat remains constant even when the vehicle is turned right, as shown by curves FL, FR.
When using the load sensors that have the characteristics shown by the curves RL, RR, FL, FR, the curve T representing the sum of the detected loads starts to fluctuate significantly when the load applied to the left and right rear sensors goes out of the detection range. In other words, the sum fluctuates when the vehicle is turned in a manner unrelated to the passenger""s weight.
As described above, when employing load sensors having a limited detection range to detect the passenger""s weight, accurate detection may not be performed depending on the running state of the vehicle. Generally, inexpensive load sensors have narrower load detection ranges and may thus fail to give accurate readings when the vehicle state changes. In other words, the employment of inexpensive sensors having narrow load detection ranges may hinder accurate load detection.
It is an object of the present invention to provide a vehicle seat weight detector that accurately detects the weight of a passenger regardless of the state of the vehicle in an inexpensive manner.
To achieve the above object, the present invention provides a weight detector for a vehicle seat for executing detection of the weight of a passenger seated on the vehicle seat. The weight detector comprises a first load sensor and a second load sensor provided respectively on opposite sides of a rear portion of the vehicle seat. Each of the first and second sensors has a predetermined detection range. The weight detector further includes a third load sensor and a fourth load sensor provided respectively on opposite sides of a front portion of the vehicle seat. Each of the third and fourth sensors has a predetermined detection range. If one of first through fourth detection values detected respectively by the first through fourth load sensors exceeds the corresponding detection range, the weight detector uses an old weight determination that was determined when the detection values were within their corresponding detection ranges.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.